1. Field of the Invention
The present invention is related to methods for adjusting resolution and refresh rate of display monitors of computer systems.
2. Prior Art
Different display monitors can operate according to different configurations. For example, the CRT (Cathode-Ray Tube) monitor for a research engineer or a corporate manager is often a new, expensive monitor with a high resolution and a high refresh rate (e.g. 85 Hz or more). In contrast, the CRT monitor for a low-level clerk or assistant is often an old, inexpensive legacy monitor with a low resolution and a low refresh rate (e.g. 60 Hz). The newer monitors support a higher refresh rate which reduces flicker, while older monitors must be refreshed at a lower rate to avoid damage to the monitor. LCD (Liquid Crystal Display) monitors have rapidly progressed to now enjoy widespread use around the world as the display apparatus of choice for PCs (Personal Computers) and other electronic equipment. An LCD produces an image on a liquid crystal surface of an LCD panel thereof by uniformly illuminating the entire liquid crystal surface area with a backlight. The backlight is a surface light source disposed behind the LCD panel. Most LCD monitors can operate with a low refresh rate (e.g. 60 Hz) without flicker, and can therefore help prevent eyestrain.
PC systems that include a monitor are set with appropriate default display configurations before sale. However, many “DIYers” (“do-it-yourselfers”) like to handpick an individual monitor to buy, either at the time they buy a PC or after they have bought a computer system. The monitor may be an old CRT monitor or an LCD monitor. In such case, if the computer system is set with a resolution and refresh rate exceeding what the CRT or LCD monitor supports, when the monitor is connected with the computer the monitor does not work or its circuitry is liable to be damaged. When this happens, a common solution adopted is to find another monitor supporting a higher resolution and refresh rate, connect the other monitor with the PC, go through the menus in a Windows control panel to manually reset the resolution and refresh rate of the computer system, and then reconnect the original monitor to the PC. This solution is highly inconvenient.
More recently, CRT monitors using the PNP (Plug-and-Play) standard have been marketed. PNP allows a PC to automatically configure a resolution and refresh rate suitable for any of a variety of different monitors. In particular, some high-resolution CRTs are capable of supporting PNP. On system initialization, the PC sends out a series of clock signals on a 15-pin VGA cable to the CRT. The CRT responds by transmitting back to the PC a 128-byte data structure called EDID (Extended Display Identification Data). The EDID contains information about the configurations and refresh rates supported by the CRT, as defined by VESA (Video Electronics Standards Association) of San Jose, Calif., USA in its “Display Data Channel Standard” dated 1996. Software in the PC reads the configuration information in the 128-byte EDID, and calculates the minimum and maximum vertical refresh rate. From the refresh rate and the current resolution desired by the user, and according to the capabilities of the graphics controller hardware, the active refresh rate can be calculated or selected by the display driver using the appropriate video BIOS function. The correct refresh rate is thus programmed when both the PC and the CRT have hardware and/or software to support auto-configuration of monitors using PNP.
Nevertheless, PNP is a relatively recent standard, and many older CRT monitors do not support the standard. In addition, many PCs do not have the necessary hardware and/or software to support auto-configuration.
To overcome this problem, U.S. Pat. No. 6,049,316 entitled PC with Multiple Video-display Refresh-rate Configurations Using Active and Default Registers and issued on Apr. 11, 2000 discloses a graphics controller sub-system for managing multiple configurations for displays on a portable PC. The graphics controller sub-system has an active register that stores a current vertical refresh rate, a vertical synchronization timer that generates a vertical synchronization pulse with a period corresponding to the current vertical refresh rate stored in the active register, and a driving means that is coupled to the vertical synchronization timer. The driving means drives the vertical synchronization pulse to an external CRT monitor. The vertical synchronization pulse resets the external CRT monitor from a last line of pixels to a first line of pixels. The active register and the default register are hardware registers on a graphics controller chip that contains the pixel transfer means.
However, the graphics controller sub-system must be installed in the computer system, which adds to the software and hardware burden of the computer system. In addition, the user may simply omit or forget to install the graphics controller sub-system before the problem actually arises. A more convenient and efficient method for adjusting a resolution and refresh rate of a display monitor is desired.